| """Rotation utilities that preserve image content without artificial borders.""" | |
| import cv2 | |
| import numpy as np | |
| import math | |
| def rotate_image(img, angle, rotation_center=None, expand=False, border_mode=cv2.BORDER_CONSTANT, border_value=0): | |
| """Rotates an image (angle in degrees) and optionally expands to avoid cropping.""" | |
| h, w = img.shape[:2] | |
| if rotation_center is None: | |
| rotation_center = (w/2, h/2) | |
| M = cv2.getRotationMatrix2D(rotation_center, angle, 1.0) | |
| if expand: | |
| abs_cos = abs(M[0, 0]) | |
| abs_sin = abs(M[0, 1]) | |
| wn = int(h * abs_sin + w * abs_cos) | |
| hn = int(h * abs_cos + w * abs_sin) | |
| M[0, 2] += wn/2 - rotation_center[0] | |
| M[1, 2] += hn/2 - rotation_center[1] | |
| else: | |
| wn, hn = w, h | |
| rotated = cv2.warpAffine( | |
| img, M, (wn, hn), borderMode=border_mode, borderValue=border_value) | |
| return rotated, M | |
| def largest_rotated_rect(w, h, angle): | |
| """Compute the largest axis-aligned rectangle within a rotated rectangle.""" | |
| if w <= 0 or h <= 0: | |
| return 0, 0 | |
| width_is_longer = w >= h | |
| side_long, side_short = (w, h) if width_is_longer else (h, w) | |
| sin_a, cos_a = abs(math.sin(angle)), abs(math.cos(angle)) | |
| if side_short <= 2.*sin_a*cos_a*side_long or abs(sin_a-cos_a) < 1e-10: | |
| x = 0.5*side_short | |
| wr, hr = (x/sin_a, x/cos_a) if width_is_longer else (x/cos_a, x/sin_a) | |
| else: | |
| cos_2a = cos_a*cos_a - sin_a*sin_a | |
| wr, hr = (w*cos_a - h*sin_a)/cos_2a, (h*cos_a - w*sin_a)/cos_2a | |
| return wr, hr | |
| def rotate_image_crop_max_area(image, angle): | |
| """Rotate image and crop to the largest inscribed rectangle (no borders). | |
| Args: | |
| image: numpy array (OpenCV image) | |
| angle: Rotation angle in degrees | |
| Returns: | |
| Rotated and cropped numpy array | |
| """ | |
| h, w = image.shape[:2] | |
| rotated, _ = rotate_image(image, angle, expand=True) | |
| wr, hr = largest_rotated_rect(w, h, math.radians(angle)) | |
| h_rot, w_rot = rotated.shape[:2] | |
| y1 = h_rot//2 - int(hr/2) | |
| y2 = y1 + int(hr) | |
| x1 = w_rot//2 - int(wr/2) | |
| x2 = x1 + int(wr) | |
| return rotated[y1:y2, x1:x2] | |